Flight controls are systems linking the pilot or autopilot module and the control surfaces that allow the trajectory of the aircraft to be modified. Flight controls notably comprise a steering element such as a joystick and a mechanical system for actuating the control surfaces. In this case, the mechanical system comprises an actuator, the actuator being an electric motor of rotary type generating a torque which compensates for the torque exerted on the control surface by external forces of aerodynamic type.
The certification authorities stipulate that the pilot must be able to override the actuator of the autopilot module at any time, in other words the pilot must be able to regain manual control, in the event of failure of the autopilot PA, for example.
One solution consists in disengaging the actuator of the flight controls when the torque exerted by said actuator, in order to compensate for the torque exerted on the control surface by the external forces or by the pilot, is greater than the threshold torque value of the actuator.
This first solution presents a drawback, since the autopilot disengages, which gives rise to violent changes of trajectory which are unpleasant for the passengers and potentially dangerous when the aircraft is at low altitude.
Disengagement of the actuator when the control surface arrives at a limit stop constitutes another drawback. It is therefore necessary to provide safety margins involving a reduction in the angle difference for movement of the control surface, which diminishes the authority of the autopilot module PA.
One improvement consists in freezing the setpoint of the actuator when the torque exerted by the actuator on the control surface to compensate for the torque exerted on the control surface by the external forces reaches the threshold torque value. This solution seeks to avoid the disengagement of the actuator by no longer operating the control surface.
However, this solution does not take into account increases in the torque exerted by the actuator to compensate for the increases in the torque exerted on the control surface by the external forces for a constant position. For example, this solution does not take into account large increases in torque exerted on the control surface in the event of an engine failure or violent gusts of wind.